Not something that should be the default, exposing everyone to the dangers.
Of course, that breaks if implementation checks the signatures in wrong moment
Assuming transport is compromised and you can only trust package signatures IS A GOOD THING. Extra security layer on top of it is nice of course but arguably if it was all https we would've never found this bug and then in case of CA compromise attacker would have plenty of bugs to use to fool apt.
The problem is that they failed ordering of validation; it should be "download from source" (of any type, remember that http(s) isn't only way) -> put into temporary dir -> validate, regardless of source used.
There are also edge cases where HTTPS does hurt you, on system without reliable time (and there is quite a few SBCs that don't have RTC) you would just not be able to download the packages at all because all certs are in future.
But yes, it should probably be a Debian installer question: use HTTPS sources or not. Debian is the universal operating system but most users running a desktop or server setup should choose YES. The setups where you really want plain HTTP sources are an edge case and users setting up such systems probably already know about their special requirements, so HTTPS sources should really be presented as the default / "if in doubt" option.